Method of making rotary gear cutters



76. METAL was 61 a rch Room 8, MAKING,

Aug. 15, 1939. R. s. DRUMMOND 2,169,632

IETHOD OF MAKING ROTARY GEAR CUTTEIS Filed Feb. 8, 1937 2 Sheets-Sheet 1w MW I w mm l 29 J I i 32 3o 1 34 i l 30 I I 23 "WW" I IN VENTOR 3ROBERT. S. DRUWOND WW AM H3 4 A TTORNEVS tearch P i mwmsms &

. Aug. 15, 1939. DRUMMQND 2,169,632

IETHOD OF MAKING ROTARY GEAR GUTTERS Filed Feb. 8, 1937 2 Sheets-Sheet 2[N VEN TOR KERT. S. DRUWGID A TTORNEYS Patented Aug. 15, 1939 UNITEDSTATES PATENT OFFICE METHOD OF MAKING ROTARY GEAR CUTTERS Robert S.Drummond, Detroit, Mich.

Application February 8, 1937, Serial No. 124,791

3 Claims. (Cl. 76-101) The invention relates to a method formanufacturing cutting tools, and more particularly to a method formaking a rotary gear cutting tool adapted for cutting or shaving gearsto obtain arranged at the roots of the teeth forming a cylindricalrelief slot. The sides of the teeth are provided with a series ofserrations l3 extending from the tops of the teeth to the cylindricalextreme accuracy, such as that shown in my holes or clearance slots It.The serrations are Patent 2,126,178, granted August 9, 1938, Rotaryclosely spaced to form intermediate lands I4 gear cutting tool. ofapproximately the same width as the width My invention is particularlydirected to the of the serrations. In one desirable form of toolmanufacture of rotary gear cutting tools from a the width of the slotsand lands are each .035 single metal blank of high speed steel. A gearinch and the depth of the serrations is also .035 cutter of this typemust be made with extreme inch. Preferably the lands i5 adjacent the endaccuracy since the accuracy of the gears which faces are greater inwidth than the intermediate are to be 'finished by the cutting tool aredelands l4, although in some instances they are pendent upon theaccuracy of the cutting tool of equal width. In the finished cuttingtool the itself. It is therefore necessary that the tooth side faces l6are ground to accurate parallelism l5 profiles of the gear cutting toolbe maintained while the side faces IQ of the teeth are accurately withinan accuracy of a few ten thousandths ground to the exact profiledesired, which while of an inch and that the profiles be capable of ingeneral is of involute curvature is nevertheless being obtained inaccordance with a predeterusually modified from true involute curvature.

) mined curve which, in many instances, is not a In the preferred methodof making the above true involute curve but some modified type describedrotary gear cutting tool, I firstpbtain adapted for a particularpurpose. In the prea blank of high speed steel forged for condensaferred form of gear cutting tool the edges of the 'tion of grain andcarefully. anneal the same. The r t t are gashed or serrated and thewidth blank must have no surface defects, seams or f of the serrationsmust be small, and I have thereother objectionable flaws. The blank isslightly i e found it necessary to devise new e o s larger than thefinal dimensions of the gear for obtaining the desired cutting 12001which lend cutter in order that it may be machined on all themse ves o te accuracy but at e same surfaces. The helical teeth are preferablyformed t me a e ap b e o being Preformed On a in the blank by a hobbingprocess leaving suffimercial production basis. cient excess metal forthe final profiling of the The P pal object Of th s inv nt n is to toothcurves. After the teeth are hobbed the Obtain improved methods formaking rotary cylindrical relief holes l2 are drilled, and these r c t 0the yp above described, although holes are of sufilcient diameter sothat the cutting the invention is also useful for the manufacture toolused in the serrating operation hereinafter :17, of other forms ofcutting tools. described will run out into the clear when trav- In thedrawings: ersing from the top to the root of the tooth.

Fig 1 s an elevation P y in section of The next operation is to form theserrations in machine I' serreting the sides of the cutter the sides ofthe teeth and this will be described teeth; in detail hereinafter.

F 2 s a c V w Of the Serra-ting $001; After the teeth are serrated theblank is heat 40 3 s an end View Of the selleting tool; treated to givethe desired hardness to the metal,

Fi 4 s a s d w of the machine shown usually a Rockwell hardness of 62 to63. The in heat treated blank may if desired be subject to F 5 is a fragy perspective View Of a a sand blast and then is finish ground. The

' rotary gear Cutter made in accordance with my side faces l6 are groundto accurate parallelism. 5

inVentiOIl; The inside diameter H of the central aperture is F 6 is afrag e ary f ce View Of e rot ry ground and the outside diameter isground sufiigear cutter. ciently to remove the surface metal.

A rotary gear cutting tool is shown in Figures The profile of the teethis then accurately 5 and 6. This cutting tool is designated by theground by a suitable mechanism. After the proreference character l0 andis preferably formed file of the teeth is obtained, the outside diameterfrom a forged high speed steel blank. The gear of the teeth is ground tothe proper addendum. teeth II are preferably helical but, in some in-The rotary gear cutter is then carefully checked stances, they may be ofthe spur type. A series for accuracy of all essential dimensions and oftransversely extending cylindrical holes I! are curvature and is readyfor use for cutting or shaving gears in gear cutting machines of thetype referred to in my above mentioned patent.

The method of making the tool about to be described is a preferredembodiment of the invention although certain modifications of theprincipal steps are contemplated. Referring to Figs. 1 to 4, it will beobserved that the tool In is accurately'centered on and secured to shaft20, the latter also having rigidly connected thereto a gear 2|.Adjustably secured to base 22 above shaft 20 is a rack 23 with whichgear 2| is adapted to mesh, while below the shaft is a second rack 24slidably guided in ways 25 on the base. Suitable driving means,indicated by crank 26 and connecting rod 21 in Fig. 1, are adapted toreciprocate rack 24. Since rack 23 is stationary and rack 24reciprocates it is apparent that gear 2| is given a rolling motionwhich, of course, is transmitted to tool Hi. Mounted on the base abovethe two racks and slidably adjustable with respect to the base is acarriage 28. Adjustment of the carriage is effected by a lead screw 29journaled in brackets 30 and having a threaded connection with thecarriage. A cutting tool 3| is secured to the carriage and is adjustablevertically thereon, an adjusting screw 32 being provided for thispurpose. The cutting tool is fixed in its adjusted position by means ofa screw 33 disposed within an elongated slot 34 in the tool.

The particular type of tool employed for cutting the serrations l3 inthe teeth of the gear finishing tool comprises a generally rectangularblock of tool steel. Adjacent an end of the block the tool is providedwith a series of projecting ribs 35 forming cutting members. These ribsare dimensioned to make the proper cut necessary to produce serrationsand lands in the teeth as desired. If the gear finishing tool is to beone having straight spur teeth the ribs on the cutting tool will ofcourse ,be parallel to the axis of the finishing tool, but if the geartool is provided with spiral teeth the lower end of the block isdistorted at an angle corresponding with the angle of the spiral teeth.The latter form of cutting tool is illustrated in Figs. 2 and 3. If nowthe finishing tool is given a rolling motion by rack 24 the cuttingedges will correspond to an element of the stationary rack. Consequentlythese edges will out a series of involute gashes in the sides of thetool teeth. The cutter is advanced progressively to make a number ofcuts until the serrations have been cut to the desired depth. Thefinishing tool can then be reversed to perform a like cutting operationon the other sides of 'the teeth. It is to be noted that the cylindricalrelief slots 12 at the base of the teeth permit the gashes or serrationsto be made to a uniform depth over the entire tooth. This is highlyadvantageous insofar as regrinding is concerned, because it is ,evidentthat regardless of the number of regrinds, the recesses always open intothe relief slots.

After the serrations have been cut in the teeth of the finishing toolthe same is finish ground to the proper profile. It is of the utmostimportance that this profile be accurate within small limits and thatthe teeth be ground to the proper curvature.

It has been previously stated herein that the finishing tool issubjected to a heat treatment after the serrations have been cut in thefaces of the teeth but prior to the grinding operations. While it isnecessary to accurately finish grind the lands between the serrationsthe serrations themselves are not ground but retain the surfacecharacteristics of the steel after heat treatment. Neither are thecylindrical surfaces of the relief slots finished but have the samesurface characteristics. This causes the surface within the serrationsto have a higher degree of hardness than the finished surfaces. Thuswhere a cutter is manufactured of heat treated steel such that thefinished surfaces have a hardness between 62 and 64 Rockwell, thehardness of the unfinished surfaces within the serrations will normallyhave a hardness as high as '70 Rockwell or more.

It has previously been pointed out that the root relief slot between theteeth of the cutter is preferably in the form of a transverselyextending cylindrical hole l2. This is of sufiic'ient size to properlyact as an avenue for the flow of oil past the cutter to assist incarrying off the chips. In normal operation oil is forced against theseholes, thereby driving the chips from the face of the tool, and thecombination of oil flow and the high speed rotation of the cuttereffectively throws off all chips. The provision of cylindrical reliefslots at the bottom of the teeth is also advantageous, for the reasonthat such slots are necessary in serrating the sides of the teeth. Therelief is of sufficient size to permit the serrating tool to run outinto a clear space at the bottom of the tooth and prevents damage to theserrating cutter.

It has been previously stated that a preferred relationship between thewidth of the serrations and lands be maintained, but generally it isdesirable to keep the widths of the lands within relatively smalldimensions to prevent burnishing action. The width of the gashes isdetermined by the amount of chip clearance desired and by the amount ofmetal which it is desired to be forced between the lands to determinethe cutting action. Where the cutter is desired for heavy rough cuttingaction, the gashes are made wider than for lighter finishing action.

In a cutter designed for normal operations, it is usual to employ notless than six serrations, nor more than twenty. Generally, it isdesirable to have the lands at the ends of the teeth somewhat wider thanthe intermediate lands to provide proper support for the cutting edges.The serrations in the cutter teeth are preferably of the sameapproximate curvature as the profile of the lands. However, it is notessential that the profile of the bottoms of the serrations should becurved, so long as they provide the proper clearance for metal duringthe cutting operation.

It will be apparent also that a rotary tool of the type shown in Figuresand 6 may have the grooves l3 therein cut by the milling cutter 15 inthe same manner as outlined above, the only difference being thatinstead of first providing the slots 12 and 1.4, the blank is providedwith the circular relief slots 12. This is illustrated in Figure 22.

What I claim as my invention is:

1. In the method of making a rotary gear finishing tool having alternatelands and grooves on the faces of the teeth thereof, the steps ofproviding enlarged slots at the roots of said teeth between said teeth,rolling said rotary tool relative to a fixed serrating tool so as tocause said fixed tool to cut grooves from the top of said teeth to theenlarged slots.

2. In the method of making a rotary gear finishing tool having alternatelands and grooves on the faces of the teeth thereof, the steps ofproviding enlarged slots at the roots of said teeth between said teeth,rolling said rotary tool back 76. METAL TOOLS &

WZPLEVENTS, MAKING,

uic afCh and forth relative to a fixed tool so as to cause said fixedtool to cut grooves from the top 01' said teeth to the enlarged slots,and limiting the amplitude of said rolling motion so that said fixedtool completes each working stroke with the cutting edges thereof in atree condition in said slots.

3. In the manufacture of gear cutting tools, the steps of formingenlarged slots between ad- 10 jacent teeth of a gear-like tool blank,supporting a serrating tool in the form of a thin blade having cuttingribs formed thereon adjacent said blank, providing a relative rollingmotion between said blank and serrating tool to cause said ribs totraverse the faces of said teeth, and limiting the amplitude of saidrolling motion such that the cutting edges of said ribs are arrested ina free condition in said slots.

ROBERT S. DRUMMOND.

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